JPH10-295004A published by the Japan Patent Office in 1998 discloses a drive force distribution control system for a four-wheel drive vehicle. The four-wheel drive vehicle includes a vehicle that drives a right rear wheel and a left rear wheel independently of each other while driving a right front wheel and a left front wheel via a differential gear, a vehicle that drives a right front wheel and a left front wheel independently of each other while driving a right rear wheel and a left rear wheel via a differential gear, and a vehicle that drives each of the four wheels independently.
The prior art system corrects a drive force of each wheel so as not to cause a variation in a yaw moment acting on the vehicle body when a tendency for slippage or wheel lock is detected in a wheel or plural wheels, or in other words when a drive force that can be transmitted from a wheel or plural wheels to the road surface is limited.
According to the prior art system, when a tendency for slippage or wheel lock is detected in any one wheel or plural wheels, a drive force of the corresponding wheel(s) is rendered to be zero. Further, the drive force is redistributed such that a sum total of all of the drive forces of the wheels and a difference in the drive forces of the right wheels and the left wheels does not vary.
If the drive force is thus redistributed, a front/aft force and a yaw moment about the center of gravity of the vehicle which are generated as the sum total of the drive forces acting on the wheels, can be maintained at the same values before and after the redistribution of the drive force even when the drive force that can be transmitted from a wheel or a plural wheels to the road surface is limited, thereby preventing the vehicle drive performance from deteriorating.